The Stripe Height (SH) of a plurality of Giant Magnetoresistive Effect (GMR) heads is collectively controlled by lapping the Air Bearing Surface (ABS) of each bar obtained by cutting each row from a wafer so that the plurality of GMR heads are aligned in one row. To control the mutual GMR height of the plurality of GMR heads of a bar and the mutual GMR height of the GMR heads of a plurality of bars to a corrective value, there are usually provided a plurality of lapping control sensors called an electric lapping guide (ELG) or a resistance lapping guide (RLG) which detects the height of a lapped ABS surface, in each bar. The lapping of the ABS surface can be controlled in response to electric signals from the ELGs or RLGs. For simplicity, the remainder of the discussion shall refer to ELGs, it being understood that the processes described herein apply to both ELGs and RLGs.
Each of the ELGs is mainly composed of a resistive element which is adjacent to the ABS surface to be lapped and extends in parallel. The ELG teaches an amount of lapping by changing its terminal voltage or its resistance due to the reduction of the height of the resistive element polished with polishing of the GMR height. Such ELG with respect to the throat height of a magnetic pole gap in an inductive head, not to the GMR height, is known by, for example, U.S. Pat. No. 4,689,877.
In manufacturing the GMR head, the ELG is generally formed in the same process of manufacturing the GMR head so as to have the same layered structure as that of the GMR head. FIG. 1 shows a multi-layered structure 100 of a conventional ELG. As shown in the figure, the conventional ELG has a multi-layered structure consisting of an optional metallic layer (shield layer) 102, an insulation layer (shield gap layer) 104, a resistive element layer (GMR sensor) 106 and lead conductors 108, which are usually made of the same material and layer thickness as those of the GMR head.
FIG. 2A shows an example of a prior art electrical lapping guide (ELG) 200, that has been used to provide an indication of Stripe Height (SH) during the lapping process. FIG. 2A depicts a slider bar 202 in cross section at a layer including the read sensor 204, and associated leads 206. A resistive element 208 is electrically connected to the controller 210 through the leads 212. During the lapping process, a current passes through the resistive element. As the lapping occurs along the lapping plane L, and while the stripe height, SH, of the read sensor is decreased, the height of the resistive element is decreased. Over time during the lapping process, changes in the resistance of the resistive element, due to the changing height, can be detected by the controller. Such changes in resistance over time is shown in FIG. 2B.
Knowing the material properties and dimensions of the resistive element relative to material properties and dimensions of the read sensor, the measured resistance Rc during the lapping process can be used to calculate an approximate height of the read sensor during the lapping process. Such a calculated height is shown over time in FIG. 2B by curves 262, 264, 266, where curves 262 and 264 are for GMR sensors and curve 266 is for an AMR sensor.
Precise stripe height control in the GMR head is achievable only when the relationship between the ELG resistance and stripe height is both known and easily measured. Using current methods, the magnetic state of the ELGs are altered by the lapping process itself. Since in a GMR head, the electrical resistance is directly related to the magnetic state, noise spikes occur during lapping, as shown in FIG. 2B. These noise spikes place a limit on the achievable resolution and accuracy of an ELG-controlled lapping process.
The imprecision caused by noise in ELG signals has been addressed, but with little success. In one method, separate, non magnetic, material are used for the ELGs. The difficulty here lies in complexity since several additional processing steps must be introduced. Also, for practical reasons, the ELG and the GMR sensor need to be patterned simultaneously using ion milling. This means that these two materials must be matched in such a way that they mill in exactly the same time. While this is workable, it constrains the choices of materials, thickness and resistances available.
Another method considered consists of installing a very large magnet in the lapping tool to suppress magnetic switching. However, this is rather impractical.
What is therefore needed is a way to reduce or eliminate the noise problem caused by GMR effects in the ELGs during lapping.